1. Field of the Invention
The present invention relates generally to a wireless charging network, and more particularly, to a differential load detecting method for detecting a wireless power receiver in a wireless power network, in which a wireless power transmitter is capable of detecting the wireless power receiver in the wireless charging network.
2. Description of the Related Art
Mobile terminals such as a mobile phone and a Personal Digital Assistant (PDA) are driven with rechargeable batteries, and the battery of the mobile terminal is charged through supplied electronic energy by using a separate charging apparatus. Separate contact terminals are generally arranged outside of the charging apparatus and the battery, which are electrically connected to each other through contact between the contact terminals.
However, since the contact terminal is outwardly protruded in such a contact type charging scheme, the contact terminal is easily contaminated and exposed to moisture, which compromises battery charging. Recently, a wireless charging or a non-contact charging technology has been developed to obviate these problems.
Such a wireless charging technology employs wireless power transmission/reception, and corresponds to, for example, a system in which a battery can be automatically charged if the battery is laid on a charging pad, without the need of a connection between the mobile phone and a separate charging connector. The wireless charging technology is widely used with wireless electrical toothbrushes and shavers, which greatly aids the portability of electronic devices since there is no need for a wired charger. Therefore, technologies related to the wireless charging technology are expected to be significantly developed in the coming age of electric cars.
The wireless charging technology largely includes an electromagnetic induction scheme using a coil, a resonance scheme using a resonance, and a Radio Frequency (RF)/microwave radiation scheme converting electrical energy to a microwave and then transmitting the microwave.
To this point, the electromagnetic induction scheme has been mainstream, but it is expected that all electronic products will eventually be wirelessly charged, in view of recent successful experiments for wirelessly transmitting power to a destination spaced away by dozens of meters through the use of microwaves.
A power transmission method through the electromagnetic induction corresponds to a scheme of transmitting electric power between a first coil and a second coil. When a magnet is moved in a coil, an induction current occurs. By using the induction current, a magnetic field is generated at a transferring end, and electric current is induced according to a change of the magnetic field so as to create energy at a reception end. The phenomenon is referred to as magnetic induction, and the electric power transmission method using magnetic induction has high energy transmission efficiency.
With respect to the resonance scheme, Prof Soljacic of the Massachusetts Institute of Technology (MIT) announced a system in which electricity is wirelessly transferred using an electric power transmission principle of the resonance scheme based on a coupled mode theory, even if a device to be charged is separated from a charging device by several meters (m). A wireless charging system of an MIT team employs a concept in physics that resonance is the tendency in which when a tuning fork oscillates at a particular frequency, a wine glass next to the tuning fork oscillates at the same frequency. The research team makes an electromagnetic wave containing electrical energy resonate instead of making sounds resonate. The resonated electrical energy is directly transferred only when there is a device having a resonance frequency and parts of electrical energy which are not used are reabsorbed into an electromagnetic field instead of being spread in the air. Thus, it is considered that the electrical energy does not affect surrounding humans or machines, unlike other electromagnetic waves.
Active research on a wireless charging scheme is currently taking place. However, standards for a wireless charging order, a search for a wireless power transmitting unit and a wireless power receiving unit, selection of a communication frequency between the wireless power transmitting unit and the wireless power receiving unit, a wireless power control, selection of a matching circuit, and communication time distribution to each wireless power receiver in one charging cycle have not been proposed.
Particularly, when the Power Transmitting Unit (PTU) detects a load, a possibility of fault detection increases if a threshold for a variation of impedance is too small, while a possibility of failing to detect a small object increases if the threshold for the variation of the impedance is too large.
Accordingly, there is a need in the art for a method in which the wireless PTU can effectively detect the load.